The present invention relates to valve timing and lift control systems in internal combustion engines and, more particularly, to a valve timing and lift control system having a first control mechanism for controlling the lift and operation angle of exhaust valves and a second control mechanism for controlling a maximum lift phase (crankshaft phase at which the lift of an associated exhaust valve or valves becomes maximum).
The valve timing and lift control system for variably controlling the opening and closing timings of exhaust valves according to an operating condition of an engine is well known in the art and disclosed, for example, in Japanese Patent Provisional Publication No. 61-190118.
The valve timing and lift control system is adapted to control the exhaust valves in such a manner as to advance the opening and closing timings of the exhaust valves while keeping the magnitude of maximum lift and operation angle constant. By advancing the opening timing of the exhaust valves, exhaust of the engine is accomplished during the time the expansion rate is small. This makes it possible to attain a higher exhaust gas temperature so that the temperature of the catalyst in the exhaust system can be raised rapidly. The catalyst thus can be activated rapidly and therefore the toxic exhaust emission from the catalytic converter can be reduced.
The present invention provides a modified valve timing and lift control system of the type described above but having additional features which will be understood as the description proceeds further.
According to an aspect of the present invention, there is provided a variable valve timing and lift control system for an internal combustion engine comprising a first control mechanism for variably controlling a valve lift and an operation angle of an exhaust valve of the engine, a second control mechanism for variably controlling a maximum lift phase of the exhaust valve, a detector for detecting an operating condition of the engine and producing a signal representative thereof, and a controller for controlling the first control mechanism and the second control mechanism in response to the signal from the detector.
According to another aspect of the present invention, there is provided a variable valve timing and lift control system for an internal combustion engine comprising a drive shaft rotatable in timed relation to a revolution of the engine, an oscillating cam mounted on the drive shaft for oscillating motion and operatively engaging an exhaust valve of the engine for opening and closing the exhaust valve when oscillates, a connecting device for drivingly connecting the drive shaft to the oscillating cam in such a manner as to convert rotation of the drive shaft to oscillating motion of the oscillating cam, a first control device for varying engagement of the oscillating cam with the exhaust valve for thereby varying a lift and an operation angle of the exhaust valve, and a second control device for varying a phase of the drive shaft and thereby varying a maximum lift phase of the exhaust valve.
These and other features and advantages of this invention will become understood from the following description with reference to the accompanying drawings.